Means for eliminating interference in grounded telegraph systems



July 5, 1932.

W.\\H. KLINE MEANS FOR ELININATING IN'I.ILRF'EfiENGE IN GROUNDED TELEGRA PH SYSTEIS Filed June 24, 1951 INVENTOR ATTORNEY.-

Patented July 5, 1932 UNITED STATES PATENT [OFFICE V 7 WILLIAM H. KLINE, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TOAMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK MEANS FOR ELIMINATING INTERFERENCE IN GRO'O'NDEB TELEGRAPH SYSTEMS Application filed June 24,

This invention relates to grounded telegraph systems, and particularly to a method and means for eliminating from such systems the efii'ects of interfering currents created by earth potential differences, power line induction and other similar sources.

In the operation of grounded telegraph systems difiiculty is sometimes experienced due to the presence in such systems of interfering currents created by sources external to the system itself, such as differences of earth potential or power line induction. Those currents created by the sources of interference afi'ect the receiving relays of the telegraph system and produce a distortion of the telegraph signals being transmitted between stations of the said system.

The present invention resides in a method and means for substantially eliminating the effect upon the receiving relays of the telegraph systemof currents created by sources of interference external to the said system.

This invention will be clearly understood from the following description when read in connection with the attached drawing showing schematically a simple formof embodiment of the invention.

In the drawing the apparatus at station A is connected to that at station B by the'line O conductors L and L the former conductor being intended to transmit signals from each station to the other, and the latter conductor being intendedfto provide a source of neutralizing current by means of which interfering currents setup in L by a source external to the system may be prevented fromafi'ecting the signals transmitted over L Connected to station A is a telegraph loop comprising a sounder 17 and a key 18, the said loop being connected. to the winding 1'-2 of the sending relay and also to the battery 19 at the station A. The sending relay has two windings 12 and 34 which windings are connected to corresponding win dings. 57-6 and 78 of the holding relay. The terminals 6 and 8 of the windings of the latter relayare both connected to the armature of the receiving relay. The contacts of the latter m relay are,connected to batteries of opposite polarity. A variable artificial line is con- 1931 I Serial No. 546,655.

nected to the terminal 3 of the sending relay, and it is designed to control the magnitude of the current traversing the windings 34 and 7 8." The armature of the sending relay is connected to "the terminal 13 of the winding 131& of the receiving relay, the otherterminal of which is connected to the line L The contacts ofthe sending relay are connected to sources of potential of opposite polarity for the transmission ofsignaling impulses over the line. The receiving relay includes also a winding 9-10 that is connectedin series with a source of potential Ell and a variable resistance 22 whereby the magnitude ofthe current flowing through the winding 9 10 and its direction may be such as to cause the armature of the receiv ing relay to move to its spacing contact whenever current in the winding 13-14 becomes zero as the result of the operation of the sending relay at station B. The winding 11--12 which is connected to the conductor'L and also to ground through the resistance 23 serves to neutralize the eifect of interfering currents upon the receiving relay at station A. The manner in which that result isaccomplished will be understood from thedescription of the operation of the system set forth hereinafter. The Winding 1516" has its terminal 15 connected to the armature of the holding relay and also to the source of potential 24, the latter connection including a choke coil 25. The terminal 16 of that winding is connected to ground. The function of the holding winding is to neutralize the eflt'ect of the biasing winding 910 and to keep the armature of the sending'relay upon its marking contact whenever the current in the winding 1314@ falls to zero as the result of the transmission of a spacing impulse from station A to station B.

The apparatus at station B and in theloop connected thereto is similar to that shown at station A, and the corresponding part-shave been given the same numerals primed.

The manner in which the circuit operates for the transmission of signals is as follows: For the transmission of a marking impulse from station A to station B the apparatus will be in the position shownin the drawing.

Thus, with the key 18 closed, current will fiow from the source 19 through the sounder 17, key 18, windings 1-2 and 56, marking contact of the receiving relay, and the negative battery to ground. Current will also flow from ground through the artificial line 20, windings 3-4 and 7-8, marking contact of the receiving relay to the negative pole of the grounded battery. Since the current through windings l2 and 56 is twice as great as that through windings 34 and 78 the armatures of the sending relay and of the holding rela will be moved to their marking contacts. ince the marking battery of the sending relay at station A is opposite in polarity to the corresponding battery at station B, current will flow over line L in the direction of the arrow, said current traversing the windings 1314 and 1814. The magnitude of that current and the direction of flow through the winding 1314 are such as to keep the armature of the receiving relay at station A upon its marking contact. At station B the current through 1314- will move the armature of the receiving relay to its marking contact, the said current being sufiicient to overcome that flowing through the biasing winding 910. WVith the armature of the receiving relay at station B upon its marking contact the current will flow from the battery 19 through the sounder 17 and the key 18', thence through the windings 12' and 5'-6 to the armature and the negative battery of the receiving relay. Current will also flow from ground through the windings 34 and 7-8' to the said armature and the negative battery of the receiving relay. Since the current through the windings 12 and 56 is twice that through the other windings'of the sending relay and the holding relay, it will maintain the armatures of the respective relays upon their marking positions. The flow of current over the circuit that includes the sounder 17 will operate the said sounder and produce a marking signal.

When the key 18 at station A is opened to transmit a spacing signal the current through the windings 12 and 56 through thescnding relay and the holding relay will drop to zero. The current throughwindings 3-4 and 7-8 will however, continueto flow in the same direction as during the transmission of a marking signal and it will cause the movement of the armatures of the respective relays to their spacing contacts. Since the polarity of thespacing battery at station A'is the same as that of the marking battery at station B, no signaling current will flow over the line conductor L and consequently, there will be no current in the wind- .ings 13-4 1 and 13''1 l.' The absence of current in the windings 1314 will permit the armature of the receiving relay at station B to be moved to its spacing contact under the influence of the current flowing through the biasing winding 910. Since the polarity of the spacing battery of the receiving relay at station B is the same as that of battery 19, current will not flow through the windings 5'6' and 1-2. Current will flow however, through windings 3-1 and 7'8, but its direction will be such as to keep the armatures of the holding relay and the sending relay respectively, upon their marking contacts. Since no current flows through the sounder 17 its armature will drop back and a spacing signal impulse will be indicated.

If, during the transmission of a spacing impulse from station A to stat-ion B, the operator of the loop at B attempted to get control of the circuit by opening the key 18, no indication of such attempt would be evident to the operator at station A. The reason for that is as follows: The opening of the key 18 eifects no change in the current flow through the windings 12' and 5-6,' inasmuch as during the transmission of a spacing impulse from station A to station B no current flows through those windings because the spacing battery of the receiving relay at station B opposes battery 19 connected with the loop of the same station. Consequently, the opening of key 18 effects no change in the position of the armatures of the holding relay and the sending relay, and therefore, there will be no abnormal operation of the sounder 17 at station A due to the opening of the key 18 when station A is sending a spacing impulse to station B. If, however, key 18 remains open and the operator at station A closes key 18 for the transmission of a marking impulse, the break signal will be transmitted and will be evidenced by the failure of the sounder 17 to indicate the transmission of a marking impulse. The reason for that is as follows: lVhen key 18 is closed, the sending relay and the holding relay at station A move their armatures to the marking positions. The armature of the sending relay thereupon connects the negative battery to the line L and current will flow through the windings of both receiving relays connected to that line. The movement of the armature of the holdin relay at station A to its marking contact e ectively shunts the holding winding 1516. The flow of current through the winding 13'14 moves the armature of the receiving relay at station B to its marking contact. Since the key 18 remains open, current will not flow through the windings 1-2 and 56 but will flow through the windings 3'-ft and 7'8. The direction of flow of current through the latter pair of windings causes the armatures of the sending relay and of the holding relayat station B to move to their spacing contacts. The movement of the armature of the sending relay connects negative battery to the line L which opposes the negative battery of the marking contact at station A and causes the signaling current in L to fall to zero. Consequently, no current flows through the winding 1314, and since the winding 1516 is ineffective, due to its being shunted, the armature of the receiving relay at station A will be moved to its spacing contact as a result of the flow of current through the biasing winding 9-10. When the armature of the receiving relay touches its spacing contact the positive battery connected to that contact will oppose the positive battery 19 and there will be no flow of current through the loop that includes the sounder 17. Consequently, its armature will not be attracted as would be the case during the transmission of a markname to this specification this 19th day of June 1931.

WILLIAM H. KLINE.

ing signal from station A to station B when p the key at station E is closed. The operator of the loop at station A accordingly knows that the other operator is attempting to get control of the circuit.

The manner in which neutralization of the effects of interfering currents is obtained is as follows: Since both of the conductors L and L have the same impedance to ground a source of interference would cause currents of the same magnitude to flow in each of the said conductors and through the windings and over apparatus connected to them. The compensating windings 11-12 and 1112' are poled to oppose the effect upon the receiving relay of a current of equal magnitude flowing through the winding l3-14 or 314. Equalization of the currents is effected by the adjustment of the resistances 23 and 23. The use of a compensating circuit such as that represented by the conductor L and the associated windings of the receiving relays and the resistances, results in substantial elimination of the effects upon the signals due to difi'erences of ground potential, 1

power line induction or other similar sources.

lVhile the invention has been disclosed in a particular form, it is to be understood that such showing is simply for illustration, and that the invention is capable of embodiment in other and difierent forms without departing from the spirit and scope of the appended claim.

What is claimed is:

In a telegraph signaling system, the combination with a pair of wires of a sending relay, a holding relay, a receiving relay having a plurality of windings one of which is connected between one of said wires and ground, the second winding is connected between the other of said wires and the armature of the sending relay, the third is connected in series with a source of current to form a biasing circuit, and a fourth is connected in series with a source of potential and the armature of the holding relay to form a holding circuit, the said first and second windings being effective- 

